The subject invention relates to the production of chemical feedstocks from coal, and more particularly to the production of ethylene from coal.
With the advent of the "energy crisis" and the concomitant realization of the generally limited nature of oil and natural gas supplies, numerous efforts were begun to develop methods whereby the abundant United States deposits of coal could be used in the production of gaseous and liquid fuels. Typical of the methods developed is the method taught by Garret, et al. in U.S. Pat. No. 3,698,882, wherein particulate coal is entrained in a non-reactive gaseous stream, pyrolyzed at a temperature of about 600.degree. F. to 1500.degree. F., at a pressure less than 10 psi, for a period of from 0.1 to 3 seconds. The pyrolysis gases are then hydrogenated to form a pipeline gas consisting essentially of methane, hydrogen, and carbon monoxide. The non-reactive gas used in the Garrett, et al. method is preferably hydrogen, but may be nitrogen, argon, methane, carbon monoxide, mixtures thereof, or other non-reactive gases.
Similarly, numerous other patents, such as U.S. Pat. Nos. 3,375,175, 3,574,065, and 4,213,826 to Eddinger, U.S. Pat. No. 4,229,185 to Sass, U.S. Pat. No. 2,709,675 to Phinney, and U.S. Pat. No. 3,855,070 to Squires, teach various methods for the production of liquid and gaseous fuels from coal. Despite the large research effort in the field of producing gaseous and liquid fuels from coal, little attention has been given to the production of chemical feedstocks, most importantly ethylene and benzene, using coal as the raw material. According to the recent report in Chemical and Engineering News (volume 61, number 4, page 13, 1983), approximately 31 billion pounds of ethylene were produced in the United States in the previous year. Ethylene is an important raw material in the plastic and polymer industries and it is anticipated that the demand for ethylene will continue to increase in the future. At present, ethylene is produced mainly through thermal and catalytic hydrocracking of ethane and other hydrocarbons.
In some of the coal pyrolysis research, researchers have reported very small yields of ethylene as an undesired side product in the production of fuels. The literature shows less than 1% ethylene formation by the pyrolysis of coal at pressures ranging from vacuum to 1000 psi with short residence times. Traditionally, the pyrolysis of coal has been carried out in inert gas atmospheres such as helium or nitrogen or in reactive gas atmospheres such as hydrogen, carbon monoxide, carbon dioxide or H.sub.2 O. A paper by I. W. Smith of CSIRO Australia (Smith, "New Approaches to Coal Pyrolysis", Proceedings of the EPRI Conference on Coal Pyrolysis, Feb. 25-26, 1981) shows 4% ethylene yield with 1% ethane and 1% propane from the pyrolysis of Pittsburg No. 8 coal at 800.degree. C. and 1 atmosphere pressure for a period of approximately 0.5 seconds.
At present, no coal conversion process is known which produces economically significant amounts of the chemical feedstocks ethylene and benzene. Applicants have found that the flash methanolysis of coal, that is the pyrolysis of coal under pressure in an atmosphere of methane, when conducted at appropriate temperatures and gas pressures, using appropriate solids residence tim and gas/solids ratios, results in economically significant yields of ethylene.
Thus, it is an object of the subject invention to provide a method for the production of substantial amounts of ethylene from coal.
It is another object of the subject invention to provide such a method which also produces substantial quantities of benzene and light oils.
It is still another object of the subject invention to provide a method for the production of ethylene from coal where substantially the only required raw material is coal.